• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.480-483
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• 2005

A roll forming process is developed for an automotive part of high strength steel. Forming rolls are designed through the plane strain elastic-plastic finite element analysis to estimate the springback. It is assumed that the process can be approximated as a series of multi-step bending processes. Then the 3D elastic-plastic finite element analysis with the solid element is carried out for the designed roll forming process. The prototype roll forming machine and the forming rolls are made and the experiments are carried out. The results of the analysis and the experiments are compared.

• Proceedings of the Korean Society of Computer Information Conference
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• 2023.01a
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• pp.289-291
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• 2023

다양한 신재생 에너지 발전 중에서 수력발전은 풍력발전과 더불어 탄소배출이 가장 적은 에너지 발전 중 하나이며, 정부의 "2050 탄소중립" 발표에 따라 근래 수력발전에 대한 관심이 증폭되고 있는 추세이다. 하지만 국내의 지리적 특성상 수력발전의 규모가 국외에 비해 소규모이며, 대규모 수력발전의 경우에도 설치가능지역이 고갈되어 다수의 소규모 수력 발전소 설치라는 방향성이 불가피한 현실이다. 이에 따라 본 연구에서는 유한요소법을 이용하여 소규모 수력발전에 가장 많이 사용되는 콘크리트 댐 형상에 대한 구조해석을 실시하고 정수압 하에서 각 콘크리트 댐의 변형 거동 및 안정성을 분석하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.49-56
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• 2012

Rupture disks are a kind of safety device in high pressure equipment and they are used to control rupture pressure in the solid rocket motor. In this paper, a series of rupture experiments was performed using rupture disks made of AISI 316L and rupture pressure of rupture disks was calculated through various assumptions in relation between elasto-plastic material properties and true stress-strain curve. Experiment and FEA indicated rupture pressure is determined by size of rupture disks. As a result of elasto-plastic analysis, only multi-linear stress-strain curve was able to calculate meaningful estimations. Experimental results also showed rupture location are decided by the size of rupture disks. Experimental and FEA results will be applied to control rupture pressure of disks.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.569-569
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• 2012

탄소나노튜브(carbon nanotubes)의 우수한 전기적, 물리적 특성으로 인해 트랜지스터, 태양전지, 고감도 센서, 나노 섬유, 고분자-탄소나노튜브 고기능 복합체 등 다양한 분야에서 이를 응용하려는 노력이 활발히 진행되고 있다. 흥미롭게도 탄소나노튜브는 구조적인 특성 (직경, 밀도, 벽의 수)에 따라 각기 다른 비표면적, 열 전도성, 전기 전도성, 접촉각, 전계방출 특성을 지닌다고 보고되고 있다. 따라서 다양한 분야의 응용을 위해서는 구조적인 특성 제어가 핵심적인 요소라고 할 수 있다. 본 연구에서는 열화학기상증착법(thermal chemical vapor deposition)을 이용하여 수직 정렬된 탄소나노튜브를 합성 하였다. 합성과정에서 압력의 변화가 탄소나노튜브의 밀도와 길이에 큰 영향을 미친다는 것을 확인하였고, 이러한 현상을 이해하기 위해 두 가지의 가능성을 고려하였다. 첫째는 압력의 변화에 따른 촉매의 형성 변화 가능성이며, 둘째는 탄화수소가스의 유입양의 변화에 따른 영향이다. 분석 결과, 동일한 압력에서 탄화수소가스의 부분압을 변화시켜 실험한 결과로부터 탄화수소의 유입양의 변화가 합성된 탄소나노튜브의 밀도에 큰 영향을 미치고 밀도가 높은 경우 길이가 긴 탄소나노튜브가 합성되는 것을 확인할 수 있었다.

• Composites Research
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• v.15 no.2
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• pp.24-31
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• 2002

In this paper, the safety of the crack existing between the load bearing part and the friction part in key slots was evaluated. The repetitive loading test considered impact damage was performed for the various crack models. Also, the probability of the crack propagation and the stress concentration at the crack tip were studied by using a FE analysis. By these method, safety of the disk was confirmed.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.225-234
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• 1998

The behavior of the underground opening depends mainly on the magnitude of the initial stress existing before excavation and on the stress redistribution due to the excavation. In the case of elasto-plastic materials such as rock mass, as the structural behavior of surrounded opening due to excavation depends on the stress path, methods and sequence of excavation have influences on the results of numerical analysis. Therefore, in order to design underground openings with large cross-section such as underground nuclear power plants, radioactive waste disposal cavems, oil storage caverns, and so on more reasonably it is desirable to consider the effect of the excavation sequence in the analysis. In this paper, the underground structure is analyzed using the finite element method and the distinct element methods with a view to review the the effect of the excavation sequence. Based on the results of the analysis the followings are discussed : influence of excavation shape and sequence, effect of structural reinforcements, influence of multi caverns.

• Computational Structural Engineering
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• v.4 no.1
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• pp.73-82
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• 1991

Recently, the finite element method has been sucessfully extended to treat the rather complex phenomena such as nonlinear buckling problems which are of considerable practical interest. In this study, a finite element program to evaluate the elasto-plastic buckling stress is developed. The Stowell's deformation theory for the plastic buckling of flat plates, which is in good agreement with experimental results, is used to evaluate bending stiffness matrix. A bifurcation analysis is performed to compute the elasto-plastic buckling stress. The subspace iteration method is employed to find the eigenvalues. The results are compared with corresponding exact solutions to the governing equations presented by Stowell and also with experimental data due to Pride. The developed program is applied to obtain elastic and elasto-plastic buckling stresses for various loading cases. The effect of different plate aspect ratio is also investigated.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.53-64
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• 2003

Many transmission towers, high-rise buildings and bridges are constructed near steep slopes and are supported by large-diameter piles. These structures may be subjected to large lateral loads, such as violent winds and earthquakes. Widely used types of foundations for these structures are pier foundations, which have large-diameters with high stiffness. The behavior of a pier foundation subjected to lateral loads is similar to that of a short rigid pile because both elements seem to fail by rotation developing passive resistance on opposite faces above and below the rotation point, unlike the behavior of a long flexible pile. This paper describes the results of several numerical studies performed with a three-dimensional finite element method (FEM) of model tests of a laterally loaded short pile located near slopes, respectively. In this paper, the results of model tests of single piles and pile groups subjected to lateral loading, in homogeneous sand with 30$^{\circ}$ slopes and horizontal ground were analyzed by the 3-D FE analyses. The pile was assumed to be linearly elastic. The sand was assumed to have non-associative characteristics, following the MC-DP model. The failure criterion is governed by the Mohr-Coulomb equation and the plastic potential is given by the Drucker-Prager equation. The main purpose of this paper is the validation of the 3-D elasto-plastic FEM by comparisons with the experimental data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.435-444
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• 2001

Even todays, accurate and efficient algorithms for the large deformation analysis of elastoplastic frame structures lack due to the complexities of kinematics, material nonlinearities and numerical methods to cater for. The author suggests appropriate beam element based upon the incremental formulation from the 3D rod theory where Cauchy stress and engineering strain are variables to incorporate plasticity equations so that objectivity may be satisfied. A rectum mapping methods which can integrate and satisfy yield criteria efficiently is suggested and a continuation method which has global convergency and quadratic speed is developed as well. leading-unloading example problems are tested and the ideas are proved to be valuable.

• Journal of the Korean Institute of Gas
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• v.1 no.1
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• pp.95-100
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• 1997

In order to predict the elastic-plastic fracture toughness for metallic materials, Finite Element Method(FEM) was used for analysis of compact tension specimen. ASTM E399 test procedure was adopted for simulation of FEM. The Load-Crack Mouth Opening Displacement curve obtained from this analysis was used to detect the crack initiation point and determine the elastic-plastic fracture toughness $J_{IC}$. In order to prove the results, they were compared with the results from previous experiments and they agree with experimental results.